The Advanced Television Systems Committee Vestigial Sideband (ATSC VSB) method, a U.S-oriented terrestrial waves digital broadcasting system, is a single carrier method and uses a field sync by 312 segment unit. Accordingly, reception performance is not good in poor channels, especially in a Doppler fading channel.
FIG. 1 is a block diagram of a transmitter/receiver of a general U.S-oriented terrestrial waves digital broadcasting system according to the ATSC digital television (DTV) standards. The digital broadcasting transmitter of FIG. 1 has a randomizer (110) for randomizing an MPEG-2 TS, an Reed-Solomon (RS) encoder (120) of a concatenated coder form for correcting errors generated by channels, an interleaver (130)(B=52,M=4), and a ⅔ rate trellis encoder (140). The encoded data are mapped in 8 level symbol and are inserted with field syncs and segment syncs as shown in FIG. 2. After that, the data are inserted with pilots, VSB-modulated, upconverted into RF and transmitted.
Meanwhile, the digital broadcasting receiver of FIG. 1 lowers the RF signal to baseband, demodulates and equalizes the lowered signal, performs channel decoding, and restores the original signal in a reverse order of the digital broadcasting transmitter. FIG. 2 shows a vestigial sideband (VSB) data frame of the U.S-oriented DTV system. In FIG. 2, one frame consists of two fields and one field has 312 data segments and field sync segment. One segment has segment syncs of four symbols and data symbols of 828 symbols.
As shown in FIG. 1, the digital broadcasting transmitter randomizes the MPG-2 TS through the randomizer (110). The randomized data are outer-coded through the RS encoder (120) which is an outer coder, and the outer-coded data are dispersed through the interleaver (130). The interleaved data are inner-coded by 12 symbol unit through the trellis encoder (140), and the inner-coded data are mapped in a 8 level symbol and inserted with the field syncs and segment syncs as shown in FIG. 2. Afterwards, the data have DC offset to generate the pilot, and are VSB-modulated, upconverted to a RF signal and transmitted.
Meanwhile, the digital broadcasting receiver of FIG. 1 converts an RF signal received through a channel into a baseband signal through a tuner/IF (not shown). The baseband signal is syncronization-detected and demodulated through a demodulator (210), and distortion by channel multipath is compensated through an equalizer (220). The equalized signal is error-corrected and decoded into symbol data through a trellis decoder (230). The decoded data, which have been dipersed by the interleaver (130) of the transmitter, are rearranged through a deinterleaver (240), and the deinterleaved data are error-corrected through an RS decoder (250). The error-corrected data are derandomized through a derandomizer (260) and output into an MPEG-2 TS.
In the VSB data frame of the U.S-oriented terrestrial waves DTV system of FIG. 2, one segment corresponds to one MPEG-2 packet. In FIG. 2, one frame consists of two fields and one field has 312 data segments and field sync segment. One segment has segment syncs of four symbols and data symbols of 828 symbols. The segment sync and field sync which are sync signals used for synchronization and equalization. The field sync and segment sync are known sequences and used as training data in the equalizer.
The VSB method of the U.S-oriented terrestrial waves digital television system of FIG. 1 is a single carrier system and there is a shortcoming that because error-correcting capacity of the trellis encoder of FIG. 3 is not so strong, energy of a large output is needed to improve a reception performance in a poor channel environment.